The long-term objective of this project is to discover basic principles governing the detection and discrimination of odorant mixtures and their components. The focus of this research will be on responses to binary odorant mixtures, which will serve as a model for more complex mixtures. A common observation in studies of mixtures of odorants or tastants is that responses to mixtures are often not predictable, even when the responses to the individual components of the mixture are known. These phenomena, termed mixture interactions, are widespread, occurring in humans as well as lower animals. The proposed project uses as the experimental animal model the spiny lobster Panulirus argus, which has proven to be an excellent system for studies of olfaction, including mixture interactions and behavioral and neural aspects of quality coding. The specific aims of this project are to: (1) identify and characterize olfactory mixture interactions for binary odorant mixtures; (2) the effects of mixture interactions on behavioral and neural discrimination of the quality of binary odorant mixtures. Mixture interactions will be identified and characterized by applying behavioral and neural responses to binary mixtures and their components to mathematical models of ligand-receptor binding. Mechanisms of mixture interactions will be identified through biochemical studies of binding of odorants to receptor sites on olfactory cell dendrites. The effect of mixture interactions on discrimination of quality of binary odorant mixtures and their components will be described by evaluating quality discrimination for binary mixtures containing components that do or do not show mixture interaction, using previously developed techniques: for neural discrimination, multivariate analysis of single-unit neurophysiological data from olfactory receptor cells and olfactory brain interneurons; for behavioral discrimination, multivariate analysis of results of differential aversive conditioning.